Treated wastewater (TWW) infiltration into non-potable aquifers has been used for decades in Western Australia for disposal and reuse. These wastewater treatment plants (WWTPs) are mostly pond systems, infiltrating secondary TWW with some activated sludge. There is no disinfection of TWW pre-infiltration. This study gave an opportunity to study the fate of Escherichia coli (E. coli) in aquifers, using compliance monitoring data (2006–2016) and is relevant if water reuse is to be implemented at these sites in the future. Microbiological water quality data (E. coli) were evaluated using an advanced statistical method able to incorporate the highly censored data at full scale operational infiltration sites. Subsurface E. coli removal from TWW was observed at all 17 infiltration sites investigated. Most sites (14) had less than six detections of E. coli in groundwater (58–100% non-detects; 7–117 samples/bore), thus the statistical method could not be applied. The observations could be used to infer between 1 to >3 log₁₀ removal for E. coli. The remaining three sites had sufficient detections for probabilistic modelling analysis, the median removal efficiency for E. coli was quantified as 96% to greater than 99%, confirming at least 1 log₁₀ removal with potential for several log₁₀ removal. Reductions could not be explained through dilution with the native groundwater alone as there was a high proportion of TWW in observation bores. The observed reductions are likely the result of bacteria retention and inactivation in the aquifer. The magnitude of microbiological water quality improvement highlights the sustainable and reliable use of the aquifer to improve water quality to levels appropriate for low- and medium-risk non-potable uses without using engineered disinfection methods.

This study investigated the influence of dissolved organic matter (DOM) additions on phosphate sorption kinetics of iron-rich sediments (39–50% hematite and goethite) from an ephemeral stream in the arid Pilbara region of sub-tropical northwest Australia. While phosphate sorption in stream sediments is known to be strongly influenced by sediment mineralogy as well as interactions with DOM, the mechanisms and significance of DOM on P-release from sediments with high sorption capacities, are largely undescribed. We assessed phosphorus (P) sorption behaviours by adding a range of solutions of known inorganic P concentrations that were amended with variable loadings of DOM derived from leachates of leaf litter to sediments from stream pools during the non-flowing phase. We compared the sorption capacity of the sediments and concurrent changes in DOM composition measured using fluorescence spectroscopy. We show that the low-dose DOM addition (~ 4 mg L⁻¹ DOC) had the effect of reducing sediment P adsorption capacity, while for the high-dose DOM addition (~ 45 mg L⁻¹ DOC), it was increased. The high-dose DOM was similar to pore water DOC and likely saturated sediment surface adsorption sites and produced P–OM–Fe complexes. This resulted in increased removal of P from solution. Sediment P sorption characteristics were well fitted to both Freundlich and Langmuir isotherm models regardless of DOC concentration. Langmuir P sorption maxima ranged from 0.106 to 0.152 mg g⁻¹. General P sorption characteristics of these iron-rich sediments did not differ among pools of contrasting hydrological connectivity. Our results show how humic-rich DOM can modulate the sediment P availability in dryland streams. Unravelling the complexities of P availability is of particular significance to further our understanding of biogeochemical processes in aquatic ecosystems where P often acts as a limiting nutrient.

Fluorinated pesticides, often referred to as "forever pesticides," are contaminants of emerging concern due to their persistent and bio-accumulative behaviour in the environment. Gaps in knowledge and technology options and research needs relevant to remediation of such pesticides are identified. Since 1990, the Australian Pesticides and Veterinary Medicines Authority (APVMA) has approved over 90 fluorinated pesticides, many of which are highly persistent and toxic in the soil-water-plant-human-environment continuum. The persistence and lipophilicity of these compounds (pesticides) pose significant risks to environments, with long-term implications to non-targeted plants, animals and human health. Though some studies have reported that metabolites and degradation products are more toxic and persistent in the environment, limited research has been undertaken to quantify the persistence, fate and transport of parent pesticides, metabolites, precursors and intermediates. The detection of ultrashort-chain PFAS (including trifluoroacetic acid) in Australian groundwater further underscores the need for targeted research on the persistence, fate and transport of both parent pesticide compounds and their degradation products in Australian ecosystems. This manuscript collates characteristics and research undertaken on 91 fluorinated pesticides used in Australia, drawing on both local and international research. We summarise current knowledge which brings emphasis to the need for synchronised research on fate and transport of these pesticides and their metabolites, risk assessment, current food chain contamination pathways and innovation in measurement and sensing of these persistent pollutants. The development of advanced analytical methods and the expansion of research into multi-compound contamination scenarios are essential for informed regulatory decisions and effective environmental management.

Natural Source Zone Deletion (NSZD) is a viable long-term management option for sites impacted by petroleum hydrocarbon fuels. NSZD rate estimation methods for petroleum mass losses often use soil gas gradients of oxygen, carbon dioxide, methane or vapour concentrations through the vadose zone. Seeking greater efficiencies, we investigated if existing short-screened wells are reliable for representative sampling of soil gases in a vadose zone undergoing NSZD. At gasoline, diesel, aviation-gasoline, crude oil and background locations, we compared soil gas compositions from three methods: (i) multilevel samplers (VZ) on three occasions over 18 months (three per location); (ii) oxygen sensors (GP) at multiple depths and tracked over 3 years (one per location); and (iii) short-screened monitoring wells (MW) across the water table (five per location) and sampled as per VZ. GP sensors showed seasonal and other variations, yielding variable NSZD estimates. Oxygen depth profiles from GP and VZ measurements showed good correspondence despite fluctuations. Oxygen, carbon dioxide and methane concentrations from the deepest sampling ports of VZ samplers correlated strongly with concentrations from adjacent MW installations, indicating in-well sampling in the field can provide reliable data. The advantages and limitations of using MW data in accelerating NSZD field assessments are outlined.